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ASAS-SN Confirmation of a Bright and Possible High-Magnification Microlensing Event

ATel #11853; Subo Dong (KIAA-PKU), K. Z. Stanek, C. S. Kochanek, T. Jayasinghe, T. A. Thompson (OSU), J. L. Prieto (Diego Portales; MAS), B. J. Shappee (Univ. of Hawaii), T. W.-S. Holoien (Carnegie)
on 14 Jul 2018; 16:51 UT
Credential Certification: Subo Dong (dongsubo@pku.edu.cn)

Subjects: Optical, Microlensing Event

Referred to by ATel #: 11882, 11883

The transient TCP J18010186-2951258 was first discovered by T. Kojima on UT 2018 07 13.494. The ASAS-SN Sky Patrol light curve (Shappee et al. 2014; Kochanek et al. 2017) suggested this to be a probable microlensing event. We take i-band follow-up images with 40cm robotic telescopes of the Las Cumbres Observatory, and the refined coordinates based on the follow-up observations are: (RA = 18:01:01.84 Dec=-29:51:23.8).

ASAS-SN has been regularly observing the field containing TCP J18010186-2951258 since 2016-03-10. The latest ASAS-SN photometry on UT 2018-07-14.1132905 shows that the source is at V = 10.73, and this is brighter than all previous ASAS-SN measurements. The light curve is consistent with single-lens microlensing models. Since we only have the rising part of the light curve, and due to the degeneracy of blending, there are a number of single-lens microlensing models compatible with data. One possible (though not unique) class of microlensing models expect the event reaching high peak magnification on around UT 2018 07 15 (see an example model here). A high-magnification microlensing event is sensitive to planets orbiting the lens star, and high-cadence photometric follow ups are encouraged in the near future.

We thank Las Cumbres Observatory and its staff for their continued support of ASAS-SN. ASAS-SN is funded in part by the Gordon and Betty Moore Foundation through grant GBMF5490 to the Ohio State University, NSF grant AST-1515927, the Mt. Cuba Astronomical Foundation, the Center for Cosmology and AstroParticle Physics (CCAPP) at OSU, and the Chinese Academy of Sciences South America Center for Astronomy (CASSACA).